1. Field of the Invention
The present invention relates to slide rails used for drawers, cassettes, etc. slidably attached to main bodies of copiers, facsimiles, printers, etc. and also used for cabinets. The invention also relates to a paper feeder and an image forming apparatus.
2. Description of the Related Art
A conventional slide rail of such a type includes a fixed rail, a movable rail, and a retainer with balls that is installed therebetween. The retainer with balls installed in the slide rail includes a plurality of balls and a retainer for rotatably holding the balls. In such a slide rail, when the movable rail slides with respect to the fixed rail, the balls in the retainer with balls roll to allow the movable rail to slide smoothly.
However, the above-described slide rail has a problem with cost because the work for assembling the retainer with balls requires much effort. To solve the above problem, Japanese Laid-open Patent Publication No. 2001-173305, for example, proposes a slide rail with no retailer with balls. As shown in FIG. 17, the conventional slide rail 101 described in Japanese Laid-open Patent Publication No. 2001-173305 includes a fixed rail 110, a movable rail 120, small-diameter roller 130, and large-diameter roller 140.
The movable rail 120 is disposed so as to be slidably fitted to the fixed rail 110. The small-diameter roller 130 is attached to the fixed rail 110, rotates about a rotation axis thereof in connection with sliding of the movable rail 120 to run on the movable rail 120. The large-diameter roller 140 is attached to the movable rail 120, rotates about a rotation axis thereof in connection with sliding of the movable rail 120 to run on the fixed rail 110.
The fixed rail 110 includes a rectangular first substrate 111, a pair of first projecting plates 112 projecting from opposite widthwise ends of the first substrate 111, and first parallel plates 113 parallel to the first substrate 111 and projecting from respective edges of the first projecting plates 112 so as to come close to each other, and these components are integrally formed. The movable rail 120 includes a rectangular second substrate 121, a pair of second projecting plates 122 projecting from opposite widthwise ends of the second substrate 121, and second parallel plates 123 parallel to the second substrate 121 and projecting from respective edges of the second projecting plates 122 so as to come close to each other, and these components are integrally formed.
However, the slide rail 101 using the small-diameter roller 130 and the large-diameter roller 140 shown in FIG. 17 has a problem in that its slidability is lower than that of the conventional slide rail using the retainer with balls. The present inventors have intensively searched for the reason for this and found that the low slidability is caused by the following reason.
In the slide rail 101 using the small-diameter roller 130 (the large-diameter roller 140), the opposite side surfaces, with respect to the direction of rotation axis, of the small-diameter roller 130 (the large-diameter roller 140) are sandwiched between the second substrate 121 (the first substrate 111) and the second parallel plates 123 (the first parallel plates 113). Therefore, the small-diameter roller 130 (the large-diameter roller 140) rotates with its side surfaces being in sliding contact with the second substrate 121 (the first substrate 111) and the second parallel plates 123 (the first parallel plates 113).
The sliding contact of the side surfaces of the small-diameter roller 130 (the large-diameter roller 140) with the second substrate 121 (the first substrate 111) and the second parallel plates 123 (the first parallel plates 113) causes frictional force, and the frictional force impairs slidability. The slide rail 101 shown in FIG. 17 will be described in detail. As shown in FIG. 18, when a supported body 150 is supported by two slide rails 101, a force indicated by arrow A2 acts on the supported body 150 because of its weight. The force indicated by arrow A2 causes falling forces indicated by arrows B2 and C2 acting on the two slide rails 101.
When the falling forces are generated, pressing forces against the upper second parallel plate 123, the upper second projecting plate 122, and the lower end of the second substrate 121, surrounded by respective dotted lines in FIG. 17, respectively are generated in the small-diameter roller 130. In addition, pressing forces against the upper first parallel plate 113, the upper first projecting plate 112, and the lower end of the first substrate 111, surrounded by respective dotted lines in FIG. 17, respectively are generated in the large-diameter roller 140.
As shown in FIG. 19, when the slide rail 101 is pulled in the direction indicated by arrow G3, the small-diameter roller 130 (the large-diameter roller 140) in contact with the upper second projecting plate 122 (the upper first projecting plate 112) rotates in the direction indicated by arrowed line I2. When the small-diameter roller 130 (the large-diameter roller 140) rotates in the direction indicated by arrowed line I2, a kinetic frictional force in the direction indicated by arrowed line J2 acts on the upper second parallel plate 123 (the upper first parallel plate 113), and a kinetic frictional force in the direction K2 acts on the lower end of the second substrate 121 (the first substrate 111). In this case, since the kinetic frictional force in the direction indicated by arrowed line J2 acts in the same direction as the direction indicated by arrow G3, i.e., the pulling direction, the resistance caused by this frictional force is small. However, since the frictional force in the direction indicated by arrowed line K2 acts in a direction opposite to the direction indicated by arrow G3, this frictional force causes large resistance. Therefore, when the frictional forces between the rails and the rollers are large, slidability deteriorates.
To improve the slidability, it is contemplated to use a resin such as polyacetal (POM: polyoxymethylene) or polyamide (PA) for the material of the rollers. Assume, for example, a case in which the rails are formed from a steel plate (SECC) generally used as a sheet metal material. Then a conventional product A in which stainless steel (SUS) was used as the roller material and a conventional product B in which a resin (for example, PA) was used as the roller material were produced, and their sliding forces with respect to the weight of the supported body 150 were measured. The results are shown in FIG. 20.
As shown in FIG. 20, when the rollers are formed from the resin, the sliding force can be reduced. However, since the allowable stress of the resin (for example, POM) is about 50 MPa, which is 1/10 of the allowable stress of the SUS (about 520 MPa), the conventional product B cannot support a high load.
When a resin increased in strength by adding glass fibers (GF) thereto (for example, PA+GF45) is used for the material of the rollers, the rollers can support a certain load or higher in high-load applications. However, with the material containing the GF added thereto, the GF appearing on the surface of the rollers scrapes the rails when the rollers slide on the rail, and the rollers and the rails wear each other. Therefore, this material is not suitable for applications that require high durability.
For example, when a metal (for example, SUS) is used as the material of the rollers, the rollers can support a high load and have high durability. However, the frictional force between the rails and the rollers becomes high, so that slidability deteriorates as shown in FIG. 20. By changing the material of the rails to SUS or by plating the SECC with Ni, surface roughness can be improved. However, with such a method, the rails are much more costly than those formed of SECC alone, so that the rails cannot be produced at low cost.
As described above, the conventional slide rails have a problem in that high-load resistance and high durability cannot be achieved simultaneously with high slidability.
In view of the above circumstances, there is need to provide a slide rail having high-load resistance and high durability and simultaneously having high slidability.